It is known to measure the levels of bacteria in fluids such as drinking water by placing a sample of the fluid in a test cell with a dye or indicator such as Resazurin or methylene blue with optionally a nutrient medium and incubating the sample at a set temperature for a minimum time. A change in dye or indicator colour indicates the presence of bacteria as the growth reduces or otherwise reacts with the indicator chemical. It is also known to add suppressants to the sample to suppress the growth of other micro-organisms than that being tested for.
Typically the colour change is monitored by eye and the incubation process takes from 14 to 48 hours. Some bacterial strains have a relatively high temperature sensitivity compared to others and the temperature may need to be maintained very close to a specific temperature in order to promote the relative growth of the species required to be detected. Thus, for instance, in some media, if it is desired to culture for the presence or absence of e. coli the required temperature of incubation may be 45° C., while if all coliform bacteria are being monitored the temperature is best set at 37° C.
The colour change is therefore a value judgement by eye, and may take considerable incubation time before it can be done.
These dye reduction tests are not considered to be reliable indicators of the type of microorganism or the quantity present. They provide a rough guide to indicate the presence or absence of bacteria.
The contamination of water, foodstuffs, additives, cosmetics, pharmaceuticals and the like by undesirable micro-organisms represents a significant threat to public health. In the past, a number of methods to monitor the presence of such micro-organisms in foodstuffs, water supplies and on food preparation surfaces have been developed.
Generally such methods rely on conventional microbiological techniques, typically including the growth of micro-organisms on selective nutrient solid support media or alternatively in selective nutrient media. Subsequent morphological and biochemical analyses are then carried out under laboratory conditions by skilled personnel.
One such technique currently carried out by the Applicant involves the use of a growth medium already stored in an evacuated UV light penetrative, clear plastics container that is sealed with a rubber septum.
The liquid sample to be tested is introduced into the container through the septum via a needle or some other form of cannulas, the pressure difference ensuring that the sample is “sucked” into the container. The sample is then incubated and tested for specific or broad types of micro-organisms using visual techniques.
By necessity, some of these testing techniques tend to be carried out on products just before they are to be sent into the marketplace and these products cannot enter the market place until the results are back from the testing laboratories.
In respect of products for human consumption, some of the methods employed to remove any residual harmful bacteria have usually just taken place and thus, not too surprisingly, the level of bacteria that the testing techniques are designed to look for is so low that the test result for this bacteria is “negative”. As such, the product is passed fit for human consumption.
However, the bacteria although present in un-detectably small quantities are nevertheless still present and multiply and under the right conditions, given the shelf life of the product, may be able to recover to the extent that the bacteria are suddenly present in sufficient quantity to cause harm once the product is consumed.
This problem of “shelf life recovery” is a serious one in many types of industry and very few solutions to this problem apart from limiting the shelf life of the product to a very small time frame have been proposed.
Furthermore, the micro-organism testing kits (of the type described above) have relatively low shelf lives “out in the field” as UV light tends to kill the growth medium contained therein. In addition, the material once tested may or may not be a bio-hazard and disposal of such materials is expensive and legislation in this area is only ever going to increase the cost of disposal of such materials.
The present invention provides a solution to these and other problems which offers advantages over the prior art or which will at least provide the public with a useful choice.